Magnetic random access memory and manufacturing method thereof

ABSTRACT

A semiconductor device includes a magnetic random access memory (MRAM) cell. The MRAM cell includes a first magnetic layer disposed over a substrate, a first non-magnetic material layer made of a non-magnetic material and disposed over the first magnetic layer, a second magnetic layer disposed over the first non-magnetic material layer, and a second non-magnetic material layer disposed over the second magnetic layer. The second magnetic layer includes a plurality of magnetic material pieces separated from each other.

RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.16/743,992 filed Jan. 15, 2020, now U.S. Pat. No. 11,004,901, which is aContinuation of U.S. patent application Ser. No. 16/019,394 filed Jun.26, 2018, now U.S. Pat. No. 10,541,269, the entire contents of each ofwhich are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a magnetic random access memory (MRAM)device and, more particularly, to an MRAM device based on a magnetictunnel junction cell formed with a semiconductor device.

BACKGROUND

An MRAM offers comparable performance to volatile static random accessmemory (SRAM) and comparable density with lower power consumption tovolatile dynamic random access memory (DRAM). Compared to non-volatilememory (NVM) flash memory, an MRAM offers much faster access times andsuffers minimal degradation over time, whereas a flash memory can onlybe rewritten a limited number of times. An MRAM cell is formed by amagnetic tunneling junction (MTJ) comprising two ferromagnetic layerswhich are separated by a thin insulating barrier, and operates bytunneling of electrons between the two ferromagnetic layers through theinsulating barrier.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic view of an MTJ MRAM cell according to anembodiment of the present disclosure.

FIG. 1B is a schematic cross sectional view of the MTJ film stackaccording to an embodiment of the present disclosure.

FIGS. 2A and 2B show schematic cross sectional views of magnetic layersof the MTJ film stack according to an embodiment of the presentdisclosure.

FIGS. 3A and 3B show operations of the MTJ film stack. FIGS. 3C and 3Dshow operations of the MTJ film stack.

FIG. 4A shows a schematic circuit diagram of an MTJ MRAM, FIG. 4B showsa schematic perspective view of a memory cell of the MTJ MRAM and FIG.4C shows a memory cell layout of the MTJ MRAM.

FIG. 5A shows a cross sectional view of a part of MTJ cell according toan embodiment of the present disclosure. FIGS. 5B and 5C show plan views(top views) of a part of MTJ cell according to an embodiment of thepresent disclosure.

FIGS. 6A, 6B, 6C, 6D and 6E show cross sectional views of a part of MTJcell according to other embodiments of the present disclosure.

FIGS. 7A, 7B, 7C, 7D and 7E show various stages of a sequentialmanufacturing process of the semiconductor device including an MRAM callaccording to an embodiment of the present disclosure.

FIGS. 8A and 8B show various stages of a sequential manufacturingprocess of the semiconductor device including an MRAM cell according toother embodiments of the present disclosure. FIGS. 8C and 8D showvarious stages of a sequential manufacturing process of thesemiconductor device including an MRAM cell according to otherembodiments of the present disclosure.

FIG. 9 shows a cross sectional view of the semiconductor deviceincluding MRAM cells according to an embodiment of the presentdisclosure.

FIGS. 10A, 10B and 10C show various stages of a sequential manufacturingprocess of the semiconductor device including an MRAM according to anembodiment of the present disclosure.

FIGS. 11A and 11B show various stages of a sequential manufacturingprocess of the semiconductor device including an MRAM according to anembodiment of the present disclosure.

FIGS. 12A and 12B show various stages of a sequential manufacturingprocess of the semiconductor device including an MRAM according toanother embodiment of the present disclosure.

FIGS. 13A and 13B show various stages of a sequential manufacturingprocess of the semiconductor device including an MRAM according toanother embodiment of the present disclosure.

FIGS. 14A and 14B show various stages of a sequential manufacturingprocess of the semiconductor device including an MRAM according toanother embodiment of the present disclosure.

FIGS. 15A and 15B show various stages of a sequential manufacturingprocess of the semiconductor device including an MRAM according toanother embodiment of the present disclosure.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the invention. Specific embodiments or examples of components andarrangements are described below to simplify the present disclosure.These are, of course, merely examples and are not intended to belimiting. For example, dimensions of elements are not limited to thedisclosed range or values, but may depend upon process conditions and/ordesired properties of the device. Moreover, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed interposing the first and second features, suchthat the first and second features may not be in direct contact. Variousfeatures may be arbitrarily drawn in different scales for simplicity andclarity. In the accompanying drawings, some layers/features may beomitted for simplification.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The device may be otherwise oriented (rotated 90 degrees orat other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly. In addition, the term“made of” may mean either “comprising” or “consisting of.” Further, inthe following fabrication process, there may be one or more additionaloperations in/between the described operations, and the order ofoperations may be changed. In the present disclosure, a phrase “one ofA, B and C” means “A, B and/or C” (A, B, C, A and B, A and C, B and C,or A, B and C), and does not mean one element from A, one element from Band one element from C, unless otherwise described.

In an operation of MRAM devices, write current, write voltage and/orwrite power are key differential factors. As the devices scale down, theability to supply driving current and voltage generally decreases. Formobile and many other applications, power consumption is also a keyfactor. The lower the write voltage, current and/or power, the moreflexible the system design becomes, and the device performance isimproved. The required current density to switch the free magnetic layer(Jc) and the resistivity of the free magnetic layer (Ra) are generallyintrinsic properties relating to the composition, structure and theinterfaces of the free magnetic layer. Therefore, reducing the writecurrent, voltage and power may be achieved by engineering thecomposition, structure and interfaces of the free magnetic layer.However, it is quite difficult. Another key differential factor is thecritical dimension (CD) of the MRAM devices. The smaller the CD, thehigher the potential storage capacity becomes. When the free magneticlayer is ideally made as a continuous single layer of magnetic metalmaterials, the whole layer is considered to be one magnetic domain withthe spins of whole layer strongly coupled together. In reality, it isunavoidable to have multiple domains in the free magnetic layer.Accordingly, in the MRAM devices, majority of the MRAM cells may haveone domain, while some of the MRAM cells may have multiple domains inthe free magnetic layer. The MRAM cells with multiple domains wouldcause tailing bits in the MRAM property distribution. With the CDshrinking, there will be more tailing bits in this category, with thetailing behavior more exacerbated, thus becoming an important roadblockfor CD scaling.

In the present disclosure, the free magnetic layer has a segregatedstructure with a plurality of magnetic material pieces separated fromeach other. Instead of a continuous single layer of magnetic metalmaterials, segregated grains, isolated by a non-magnetic segregationlayer, are used as the free magnetic layer.

FIG. 1A is a schematic view of an MTJ MRAM cell according to anembodiment of the present disclosure, and FIG. 1B is a schematic crosssectional view of the MTJ film stack. The MTJ film stack 100 is disposedbetween a lower metal layer Mx and an upper metal layer My of asemiconductor device. The metal layers Mx and My are used to connect oneelement to another element in a semiconductor device formed at adifferent level above a substrate. Further, the lower metal layer Mx iscoupled to a switching device SW, which can be formed by a MOS FETincluding, but not limited to, a planar MOS FET, a fin FET, agate-all-around (GAA) FET, or any other switching devices. A controlterminal (e.g., a gate terminal of FET) of the switching device iscoupled to a word line. The upper metal layer My is coupled to a bitline. In some embodiments, the switching device SW is disposed betweenthe upper metal layer My and the bit line.

The MTJ film stack 100 shown in FIG. 1B includes a first electrode layer110 coupled to the lower metal layer Mx and a second electrode layer 155coupled to the upper metal layer My. An MTJ functional layer 101 isdisposed between the first electrode layer 110 and the second electrodelayer 155.

The MTJ functional layer 101 includes a second pinned magnetic layer130, a free magnetic layer 140, and a tunneling barrier layer 135 madeof a non-magnetic material and disposed between the second pinnedmagnetic layer 130 and the free magnetic layer 140. The free magneticlayer 140 and the second pinned magnetic layer 130 include one or moreferromagnetic materials that can be magnetically oriented, respectively.The second pinned magnetic layer 130 is configured such that themagnetic orientation is fixed and will not respond to a typical magneticfield. In some embodiments, the thickness of the free magnetic layer 140is in a range from about 0.8 nm to about 1.5 nm. In some embodiments,the thickness of the second pinned layer 130 is in a range from about0.8 nm to about 2.0 nm.

The tunneling barrier layer 135 includes a relatively thin oxide layercapable of electrically isolating the free magnetic layer 140 from thesecond pinned magnetic layer 130 at low potentials and capable ofconducting current through electron tunneling at higher potentials. Insome embodiments, the tunneling barrier layer 135 includes magnesiumoxide (MgO) having a thickness in a range from about 0.5 nm to about 1.2nm.

The MTJ functional layer 101 further includes an antiferromagnetic layer125, as shown in FIG. 1B. The anti-ferromagnetic layer 125 is used tofix the magnetic orientation of the second pinned magnetic layer 130.The antiferromagnetic layer 125 includes ruthenium (Ru) or any othersuitable antiferromagnetic material. In some embodiments, the thicknessof the antiferromagnetic layer 125 is in a range from about 0.4 nm toabout 1.0 nm.

The MTJ functional layer 101 further includes a first pinned magneticlayer 120 and a second pinned magnetic layer 130 both including one ormore magnetic materials, as shown in FIG. 1B.

The first electrode layer 110 is formed on the lower metal layer Mx madeof, for example, Cu, Al, W, Co, Ni, and/or an alloy thereof, and theupper metal layer My made of, for example, Cu, Al, W, Co, Ni, and/or analloy thereof, is formed on the second electrode layer 155.

The second pinned magnetic layer 130 includes multiple layers ofmagnetic materials. In some embodiments, as shown in FIG. 2A, the secondpinned magnetic layer 130 includes four layers 1301, 1302, 1303 and1304, where the layer 1304 is in contact with the tunneling barrierlayer 135 and the layer 1301 is in contact with the antiferromagneticlayer 125. In some embodiments, the layer 1301 (the bottommost layer)includes a multilayer structure of cobalt (Co) and platinum (Pt). Insome embodiments, a thickness of the cobalt layer is in a range fromabout 0.3 nm to about 0.6 nm and a thickness of the platinum layer is ina range from about 0.2 nm to about 0.5 nm. The thickness of the cobaltlayer can be the same as or greater than the platinum layer. The cobaltlayers and the platinum layers are alternately stacked such that thetotal thickness of the layer 1301 is in a range from about 2.0 nm toabout 5.0 nm in some embodiments. The layer 1302 includes a cobalt layerhaving a thickness in a range from about 0.4 nm to about 0.6 nm. Incertain embodiments, the layer 1301 includes the cobalt layer and thelayer 1302 is the multilayer of the cobalt layers and the platinumlayers as set forth above. In this disclosure, an “element” layergenerally means that the content of the “element” is more than 99%.

The layer 1303 is a spacer layer. The thickness of the spacer layer 1303is in a range from about 0.2 nm to about 0.5 nm in some embodiments. Thelayer 1304 includes a cobalt iron boron (CoFeB) layer, acobalt/palladium (CoPd) layer and/or a cobalt iron (CoFe) layer. Thethickness of the layer 1304 is in a range from about 0.8 nm to about 1.5nm in some embodiments.

The first pinned magnetic layer 120 includes multiple layers of magneticmaterials. In some embodiments, as shown in FIG. 2B, the first pinnedmagnetic layer 120 includes two layers 1201 and 1202, where the layer1202 is in contact with the antiferromagnetic layer 125. In someembodiments, the layer 1201 includes a multilayer structure of cobalt(Co) and platinum (Pt). In some embodiments, a thickness of the cobaltlayer is in a range from about 0.3 nm to about 0.6 nm and a thickness ofthe platinum layer is in a range from about 0.2 nm to about 0.5 nm. Thethickness of the cobalt layer can be the same as or greater than theplatinum layer. The cobalt layers and the platinum layers arealternately stacked such that the total thickness of the layer 1201 isin a range from about 5.0 nm to about 10.0 nm in some embodiments. Thelayer 1202 includes a cobalt layer having a thickness in a range fromabout 0.4 nm to about 0.6 nm.

The free magnetic layer 140 includes a cobalt iron boron (CoFeB) layer,a cobalt/palladium (CoPd) layer and/or a cobalt iron (CoFe) layer havinga thickness in a range from about 0.1 nm to about 2.0 nm in someembodiments. In other embodiments, the thickness of the free magneticlayer 140 is in a range from 0.2 nm to 1.5 nm. In certain embodiments,the thickness of the free magnetic layer 140 is in a range from 0.2 nmto 1.0 nm. The detailed structures of the free magnetic layer 140 willbe described later.

The MTJ functional layer 101 further includes a seed layer 115 formed onthe first electrode layer 110, a capping layer 145 formed on the freemagnetic layer 140, and a diffusion barrier layer 150 formed on thecapping layer 145, as shown in FIG. 1B. The capping layer 145 includes adielectric material, such as magnesium oxide, silicon oxide or aluminumoxide, and has a thickness in a range from about 0.5 nm to about 1.5 nmin some embodiments. The diffusion barrier layer 150 is made of the sameas or different material than the capping layer 145, and includes adielectric material, such as magnesium oxide, silicon oxide or aluminumoxide, and has a thickness in a range from about 0.5 nm to about 1.5 nmin some embodiments. When the diffusion barrier layer 150 is made of thesame material as the capping layer, either one of the diffusion barrierlayer 150 or the capping layer 145 is omitted.

The first electrode layer 110 includes a conductive material, such as ametal (e.g., Ta, Mo, Co, Pt, Ni), to reduce the resistance of the firstpinned magnetic layer 120, especially for programming. The secondelectrode layer 155 also includes a conductive material, such as ametal, to reduce the resistivity during reading.

The pinned magnetic layer, the free magnetic layer and theantiferromagnetic layer can be formed by physical vapor deposition(PVD), molecular beam epitaxy (MBE), pulsed laser deposition (PLD),atomic layer deposition (ALD), electron beam (e-beam) epitaxy, chemicalvapor deposition (CVD), or derivative CVD processes, including lowpressure CVD (LPCVD), ultrahigh vacuum CVD (UHVCVD), reduced pressureCVD (RPCVD), or any combinations thereof, or any other suitable filmdeposition method. The tunneling barrier layer and the diffusion barrierlayer can also be formed by CVD, PVD or ALD or any other suitable filmdeposition method.

FIGS. 3A-3D show a memory operation of MTJ cells. As shown in FIGS.3A-3D, the MTJ cell includes a pinned magnetic layer 10, a tunnelingbarrier layer 15 and a free magnetic layer 20. The pinned magnetic layer10 corresponds to the second pinned magnetic layer 130 or thecombination of the first pinned magnetic layer 120, theantiferromagnetic layer 125 and the second pinned magnetic layer 130 ofFIG. 1B. The tunneling barrier layer 15 corresponds to the tunnelingbarrier layer 135 of FIG. 1B and the free magnetic layer 20 correspondsto the free magnetic layer 140 of FIG. 1B. In FIGS. 3A-3D, the remaininglayers are omitted. A current source 30 is coupled to the MTJ structurein series. The cell size (the largest width of the MTJ stack) in planview is in a range from about 10 nm to about 100 nm in some embodiments.

In FIG. 3A, the pinned magnetic layer 10 and the free magnetic layer 20are magnetically oriented in opposite directions. In some embodiments,the spin directions of the pinned magnetic layer 10 and the freemagnetic layer 20 are parallel to the film stack direction(perpendicular to the surface of the films). In FIG. 3B, the pinnedmagnetic layer 10 and the free magnetic layer 20 are magneticallyoriented in the same direction. In other embodiments, the spindirections of the pinned magnetic layer 10 and the free magnetic layer20 are perpendicular to the film stack direction (parallel with thesurface of the films), as shown in FIGS. 3C and 3D. In FIG. 3C, thepinned magnetic layer 10 and the free magnetic layer 20 are magneticallyoriented in opposite directions, while in FIG. 3D, the pinned magneticlayer 10 and the free magnetic layer 20 are magnetically oriented in thesame direction.

If the same current value Ic is forced to flow through the MTJ cell bythe current source 30, it is found that the cell voltage V₁ in the caseof FIG. 3A (or FIG. 3C) is larger than the cell voltage V₂ in the caseof FIG. 3B (or FIG. 3D), because the resistance of an opposite-orientedMTJ cell shown in FIG. 3A (or FIG. 3C) is greater than the resistance ofa same-oriented MTJ cell shown in FIG. 3B (or FIG. 3D). Binary logicdata (“0” and “1”) can be stored in an MTJ cell and retrieved based onthe cell orientation and resulting resistance. Further, since the storeddata does not require a storage energy source, the cell is non-volatile.

FIG. 4A shows a schematic circuit diagram of an MTJ MRAM array 50. Eachmemory cell includes an MTJ cell Mc and a transistor Tr, such as a MOSFET. The gate of the transistor Tr is coupled to one of word lines WL₁ .. . WLm and a drain (or a source) of the transistor Tr is coupled to oneend of the MTJ cell Mc, and another end of the MTJ cell is coupled toone of bit lines BL_(n), BL_(n+1) and BL_(n+2). Further, in someembodiments, signal lines (not shown) for programming are providedadjacent to the MTJ cells.

A memory cell is read by asserting the word line of that cell, forcing areading current through the bit line of that cell, and then measuringthe voltage on that bit line. For example, to read the state of a targetMTJ cell, the word line is asserted to turn ON the transistor Tr. Thefree magnetic layer of the target MTJ cell is thereby coupled to one ofthe fixed potential lines SL_(n), SL_(n+1) and SL_(n+2), e.g., theground, through the transistor Tr. Next, the reading current is forcedon the bit line. Since only the given reading transistor Tr is turnedON, the reading current flows through the target MTJ cell to the ground.The voltage of the bit line then measured to determine the state (“0” or“1”) of the target MTJ cell. In some embodiments, as shown in FIG. 4A,each MTJ cell has one reading transistor Tr. Therefore, this type ofMRAM architecture is called 1T1R. In other embodiments, two transistorsare assigned to one MTJ cell, forming a 2T1R system. Other cell arrayconfigurations can be employed.

FIG. 4B shows a schematic perspective view of a memory cell of the MTJMRAM and FIG. 4C shows a memory cell layout of the MTJ MRAM.

As shown in FIGS. 4B and 4C, the MTJ cell MTJ is disposed above aswitching device SW, such as a MOS FET. The gate Gate of the MOSFET is aword line WL or coupled to a word line formed by a metal layer. Thebottom electrode Mx of the MTJ cell is coupled to a drain of the MOS FETformed in an active region AR, and a source of the MOS FET formed in theactive region AR is coupled to the source line SL. The upper electrodeof the MTJ cell is coupled to a bit line BL. In some embodiments, thesource line SL can be formed by metal layers M1 and M2, and the bit lineBL can be formed by a metal layer M3. In certain embodiments, one ofmore metal wirings is a single device layer, and in other embodiments,one or more metal wirings are two or more device layers.

FIG. 5A shows a cross sectional view of a part of MTJ cell according toan embodiment of the present disclosure. Material, configuration,dimensions and/or processes the same as or similar to the foregoingembodiments described with FIGS. 1A-4C may be employed in the followingembodiments, and detailed explanation thereof may be omitted.

FIG. 5A shows a pinned magnetic layer (second pinned magnetic layer)130, a tunneling barrier layer 135, a free magnetic layer 140 and acapping layer 145. In the present disclosure, the free magnetic layer140 includes a plurality of magnetic material pieces 140P separated fromeach other by a separation layer 142. In the present disclosure, thefree magnetic layer 140 is not a single, integrated laminated layer. Insome embodiments, the separation layer 142 is made of a non-magneticmaterial. In certain embodiments, the separation layer 142 is made of adielectric material, such as magnesium oxide, silicon oxide or aluminumoxide.

In some embodiments, a non-magnetic material of the separation layer 142is the same as the non-magnetic material of the tunneling barrier layer135. In other embodiments, the non-magnetic material of the separationlayer 142 is different from the non-magnetic material of the tunnelingbarrier layer 135. In some embodiments, the non-magnetic material of theseparation layer 142 is the same as the non-magnetic material of thecapping layer 145. In other embodiments, the non-magnetic material ofthe separation layer 142 is different from the non-magnetic material ofthe capping barrier layer 135. In certain embodiments, the non-magneticmaterial of the separation layer 142, the non-magnetic material of thetunneling barrier layer 135 and the non-magnetic material of the cappinglayer 145 are the same. Further, in some embodiments, as shown in FIG.5A, the separation layer 142 is formed in direct contact with thetunneling barrier layer 135. The separation layer 142 is amorphous insome embodiments, and is single or poly crystalline in otherembodiments.

As shown in FIGS. 5B and 5C, the plurality of magnetic material pieces140P are islands surrounded by the separation layer 142. In someembodiments, the shapes and/or sizes of the islands 140P are uniform.The size is a maximum width of the piece of magnetic material 140P, insome embodiments. In some embodiments, the variation (3σ) of the sizesis less than about 0.2 nm. The variation 3σ is calculated from, forexample, measurements of 10 magnetic material pieces 140P.

In other embodiments, the shapes and/or sizes of the islands 140P arerandom. In some embodiments, the shapes are circular, oval, acloud-shape and/or an undefined shape, as shown in FIG. 5C. The size ofthe islands 140P is the maximum width of the island in plan view.

In some embodiments, the average size of each of the plurality ofmagnetic material pieces 140P in plan view is in a range from about 0.5nm to about 20 nm, and is in a range from about 1 nm to about 10 nm inother embodiments. In some embodiments, the variation (3σ) of the sizesis less than about 1 nm. The variation 3σ is calculated from, forexample, measurements of 10 magnetic material pieces 140P.

In some embodiments, the average space between adjacent magneticmaterial pieces in plan view are in a range from about 0.2 nm to about10 nm, and is in a range from about 1 nm to about 5 nm in otherembodiments.

The thickness, which is the average height of the plurality of pieces(e.g., 10 pieces) of magnetic material, is in a range from about 0.2 nmto about 1.5 nm. In certain embodiments, the thickness of the freemagnetic layer 140 is in a range from about 0.2 nm to about 1.0 nm. Insome embodiments, the heights of the plurality of magnetic materialpieces are random.

In some embodiments, the magnetic material pieces 140P have randommagnetic directions. In certain embodiments, each of the magneticmaterial pieces 140P has one magnetic domain and/or is made of a singlecrystal.

In some embodiments, a ratio of areas of the plurality of magneticmaterial pieces 140P covering the first non-magnetic layer in plan viewto an area of the tunneling barrier layer 135 within one MRAM cell is ina range from about 0.5 to about 0.9. In other words, about 50-90% of thesurface of the tunneling barrier layer 135 within one MRAM cell iscovered by the free magnetic layer 140P. In other embodiments, the ratiois in a range from about 0.6 to about 0.8.

FIGS. 6A-6E show cross sectional views of a part of MTJ cell accordingto other embodiments of the present disclosure.

In some embodiments, the magnetic material pieces 140P have a taperedcolumnar shape having a width at the top smaller than a width at thebottom, as shown in FIG. 6A. In some embodiments, the magnetic materialpieces 140P have a tapered columnar shape having a width at the toplarger than a width at the bottom, as shown in FIG. 6B. In otherembodiments, the magnetic material pieces 140P have a columnar barrelshape having the largest width at the middle, as shown in FIG. 6C. Inother embodiments, the magnetic material pieces 140P have a columnarpincushion shape having the smallest width at the middle, as shown inFIG. 6D. In some embodiments, cross sectional shapes of the magneticmaterial pieces 140P are random, as shown in FIG. 6E.

FIGS. 7A-7E show various stages of a sequential manufacturing process ofthe semiconductor device including an MRAM call according to anembodiment of the present disclosure. It is understood that additionaloperations can be provided before, during, and after the processes shownby FIGS. 7A-7E, and some of the operations described below can bereplaced or eliminated, for additional embodiments of the method.Material, configuration, dimensions and/or processes the same as orsimilar to the foregoing embodiments described with FIGS. 1A-6E may beemployed in the following embodiments, and detailed explanation thereofmay be omitted.

As shown in FIG. 7A, a first magnetic layer 130 is formed over asubstrate (e.g., 201 shown in FIG. 9), and a first non-magnetic materiallayer 135 is formed over the first magnetic layer 130. The firstmagnetic layer 130 can be formed by PVD including a sputtering method,ALD and/or CVD or any other film formation methods. The firstnon-magnetic material layer 135 can be formed by CVD, PVD or ALD or anyother suitable film deposition method.

Next, as shown in FIG. 7B, a second magnetic layer 140 is formed overthe first non-magnetic material layer 135. The second magnetic layer 140can be formed by CVD, PVD or ALD or any other suitable film depositionmethod. In certain embodiments, a sputtering method is used. In someembodiments, a film deposition rate is in a range from about 0.01 nm/secto about 0.5 nm/sec. When the thickness of the second magnetic layer 140is less than a critical thickness, the second magnetic layer 140 canhave a plurality of magnetic material pieces (islands), as shown in FIG.7B.

Subsequently, a second non-magnetic material layer 142 is formed overthe second magnetic layer 140, as shown in FIG. 7C. Since the secondmagnetic layer 140 is formed of islands, the second non-magneticmaterial layer 142 fills the spaces between the magnetic material pieces(islands) and is formed in direct contact with exposed surface portionsof the first non-magnetic material layer 135. In some embodiments, thesecond non-magnetic material layer 142 is formed at the level of thehighest portion of the second magnetic layer 140 or lower. In otherembodiments, the second non-magnetic material layer 142 is formed to ahigher level than the highest portion of the second magnetic layer 140,and thus the plurality of pieces of magnetic materials are fullyembedded in the second non-magnetic material layer 142. The secondnon-magnetic material layer 142 can be formed by CVD, PVD or ALD or anyother suitable film deposition method.

Further, as shown in FIG. 7D, a third non-magnetic material layer 145,as the capping layer, is formed over the second non-magnetic materiallayer 142 and the second magnetic layer 140. The third non-magneticmaterial layer 145 can be formed by CVD, PVD or ALD or any othersuitable film deposition method.

Subsequently, the third non-magnetic material layer 145, the secondnon-magnetic material layer 142, the second magnetic layer 140, thefirst non-magnetic material layer 135 and the first magnetic layer 130are patterned by using one or more lithography and etching operations,as shown in FIG. 7E. In some embodiments, before the patterning, one ormore additional layers are formed over the third non-magnetic materiallayer 145.

FIGS. 8A and 8B show various stages of a sequential manufacturingprocess of the semiconductor device including an MRAM cell according toother embodiments of the present disclosure.

In some embodiments, after the second magnetic layer 140 is formed, athird (or the second) non-magnetic layer 145 is formed is a single filmformation operation, so that the plurality of pieces of magneticmaterials are fully embedded in the third (second) non-magnetic materiallayer 145. Then, as shown in FIG. 8B, the third (second) non-magneticmaterial layer 145, the second magnetic layer 140, the firstnon-magnetic material layer 135 and the first magnetic layer 130 arepatterned by using one or more lithography and etching operations.

FIGS. 8C and 8D show various stages of a sequential manufacturingprocess of the semiconductor device including an MRAM cell according toother embodiments of the present disclosure.

In some embodiments, after the second magnetic layer 140 is formed, anannealing operation is performed. When the second magnetic layer 140 isformed as a non-segregated layer 141 as shown in FIG. 8C, by theannealing operation, the non-segregated layer becomes a plurality ofmagnetic material pieces 140P, as shown in FIG. 8D.

In some embodiments, the annealing temperature is in a range from about400° C. to about 800° C. In certain embodiments, the annealingtemperature is in a range from about 400° C. to about 600° C. for about5 min to about 90 min. In other embodiments, the annealing temperatureis in a range from about 600° C. to about 800° C. for about 5 sec toabout 30 min. The annealing operation can be lamp annealing using aninfrared lamp or laser annealing.

In some embodiments, the thickness of the second magnetic layer 140 canbe measured by wavelength dispersive X-ray fluorescence (WDXRF).

FIG. 9 shows a cross sectional view of an MTJ MRAM according to anembodiment of the present disclosure. Material, configuration,dimensions and/or processes the same as or similar to the foregoingembodiments described by FIGS. 1A-4D may be employed in the followingembodiments, and detailed explanation thereof may be omitted.

As shown in FIG. 9, the MTJ cells of an MRAM are disposed over asubstrate 201. The cell size (the largest width of the MTJ stack) inplan view is in a range from about 10 nm to about 100 nm in someembodiments.

The MTJ cells of an MRAM are disposed over a substrate 201. In someembodiments, the substrate 201 includes a suitable elementalsemiconductor, such as silicon, diamond or germanium; a suitable alloyor compound semiconductor, such as Group-IV compound semiconductors(silicon germanium (SiGe), silicon carbide (SiC), silicon germaniumcarbide (SiGeC), GeSn, SiSn, SiGeSn), Group III-V compoundsemiconductors (e.g., gallium arsenide (GaAs), indium gallium arsenide(InGaAs), indium arsenide (InAs), indium phosphide (InP), indiumantimonide (InSb), gallium arsenic phosphide (GaAsP), or gallium indiumphosphide (GaInP)), or the like. Further, the substrate 201 may includean epitaxial layer (epi-layer), which may be strained for performanceenhancement, and/or may include a silicon-on-insulator (SOI) structure.

Various electronic devices (not shown), such as transistors (e.g., MOSFET), are disposed on the substrate 201. The MOS FET may include aplanar MOS FET, a fin FET and/or a gate-all-around FET. A firstinterlayer dielectric (ILD) layer 210 is disposed over the substrate 201to cover the electronic devices. The first ILD layer 210 may be referredto as an inter-metal dielectric (IMD) layer. The first ILD layer 210includes one or more dielectric layers, such as silicon oxide, siliconnitride, silicon oxynitride, fluorine-doped silicate glass (FSG), low-kdielectrics such as carbon doped oxides, extremely low-k dielectricssuch as porous carbon doped silicon dioxide, a polymer such aspolyimide, combinations of these, or the like. In some embodiments, thefirst ILD layer 210 is formed through a process such as CVD, flowableCVD (FCVD), or a spin-on-glass process, although any acceptable processmay be utilized. Subsequently, a planarization process, such as chemicalmechanical polishing (CMP) and/or an etch-back process, or the like isperformed.

Further, a lower metal wiring 213 is formed by, for example, a damasceneprocess. The lower metal wiring 213 includes one or more layers ofconductive material, such as Cu, a Cu alloy, Al or any other suitableconductive materials. Each of the MTJ cells is disposed over the lowermetal wiring 215, as shown in FIG. 9. Although FIG. 9 shows three MTJcells, the number of the MTJ cells is not limited to three.

As shown in FIG. 9, a first insulating layer 220 as an etch stop layeris formed on the first ILD layer 210. In some embodiments, the firstinsulating layer 220 includes a material different from the first ILDlayer 210 and includes silicon carbide, silicon nitride, aluminum oxideor any other suitable material. The thickness of the first insulatinglayer 220 is in a range from about 10 nm to about 25 nm in someembodiments.

A second ILD layer 225 is formed over the first insulating layer 220.The second ILD layer includes one or more dielectric layers, such assilicon oxide, silicon nitride, silicon oxynitride, fluorine-dopedsilicate glass (FSG), low-k dielectrics such as carbon doped oxides,extremely low-k dielectrics such as porous carbon doped silicon dioxide,a polymer such as polyimide, combinations of these, or the like. In someembodiments, the material for the first ILD layer 210 and the materialfor the second ILD layer 225 are the same. In other embodiments,different dielectric materials are used for the first ILD layer 210 andthe second ILD layer 225.

A via contact 219 is formed in contact with the lower metal wiring 215and passing through the second ILD layer 225 and the first etch stoplayer 220 in some embodiments. In some embodiments, the via contact 219includes a liner layer 215 and a body layer 217. The liner layer 215includes one or more layers of Ti, TiN, Ta or TaN, or other suitablematerial, and the body layer 217 includes one or more layers of W, Cu,Al, Mo, Co, Pt, Ni, and/or an alloy thereof or other suitable material,in some embodiments.

An MRAM cell includes a bottom electrode 254, an MTJ film stack 255 anda top electrode 256, as shown in FIG. 9. The bottom electrode 254, theMTJ film stack 255 and the top electrode 256 correspond to the firstelectrode 110, the MTJ functional layer 101 and the second electrode 155of FIG. 1B. The MRAM cell structure has a tapered shape as shown in FIG.9. The width of the MRAM cell structure at the bottom (the bottomelectrode 254) is greater than the width at the top (the top electrode256). The thickness of the bottom electrode 254 is in a range from about5 nm to about 20 nm in some embodiments. The thickness of the MTJ filmstack 255 is in a range from about 15 nm to about 50 nm in someembodiments.

In some embodiments, a first insulating cover layer 227 as a sidewallspacer layer is formed on opposing side walls of the MRAM cellstructure. The first insulating cover layer 227 includes one or morelayers of insulating material. In some embodiments, a nitride-basedinsulating material is used. In certain embodiments, the nitride-basedinsulating material is a silicon nitride-based insulating material, suchas silicon nitride, SiON, SiCN and SiOCN. The thickness T1 of the firstinsulating cover layer 227 is in a range from about 5 nm to about 30 nmin some embodiments, and is in a range from about 10 nm to about 20 nmin other embodiments.

Further, a second insulating cover layer 280 is formed over the firstinsulating cover layer 227. The second insulating cover layer 280includes one or more layers of an insulating material different from thefirst insulating cover layer 227. In some embodiments, an aluminum-basedinsulating material is used. In certain embodiments, the aluminum-basedinsulating material includes aluminum oxide, aluminum nitride, aluminumoxynitride, aluminum carbide and/or aluminum oxycarbide. The thicknessT2 of the second insulating cover layer 280 is smaller than thethickness T1 of the first insulating cover layer in some embodiments.The thickness T2 is in a range from about 1 nm to about 10 nm in someembodiments, and is in a range from about 3 nm to about 5 nm in otherembodiments.

Further a third ILD layer 230 is disposed in spaces between the MRAMcell structures. The third ILD layer 230 includes one or more dielectriclayers, such as silicon oxide, silicon nitride, silicon oxynitride,fluorine-doped silicate glass (FSG), low-k dielectrics such as carbondoped oxides, extremely low-k dielectrics such as porous carbon dopedsilicon dioxide, a polymer such as polyimide, combinations of these, orthe like. In some embodiments, the material for the first ILD layer 210,the material for the second ILD layer 225 and the material for the thirdILD layer 230 are the same. In other embodiments, at least two of themare made of different dielectric materials.

Further, a fourth ILD layer is disposed over the third ILD layer 230. Insome embodiments, the fourth ILD layer is a multiple layer structure andincludes a first dielectric layer 235 as an etch stop layer formed onthe third ILD layer 230, a second dielectric layer 237 formed on thefirst dielectric layer 235 and a third dielectric layer 240 formed onthe second dielectric layer. In other embodiments, the fourth ILD layeris a two-layer structure without one of the first or second dielectriclayers.

In some embodiments, the first dielectric layer 235 and seconddielectric layer 237 are made of a different material than the thirddielectric layer 240 and include one or more layers of silicon nitride,SiON, SiOCN, SiCN, SiC or any other suitable material. In someembodiments, the first dielectric layer 235 and second dielectric layer237 are made of different materials from each other.

The third dielectric layer 240 includes one or more dielectric layers,such as silicon oxide, silicon nitride, silicon oxynitride,fluorine-doped silicate glass (FSG), low-k dielectrics such as carbondoped oxides, extremely low-k dielectrics such as porous carbon dopedsilicon dioxide, a polymer such as polyimide, combinations of these, orthe like.

In some embodiments, the material for the first ILD layer 210, thematerial for the second ILD layer 225, the material for the third ILDlayer 230 and the material for the third dielectric layer 240 are thesame. In other embodiments, at least two of them are made of differentdielectric materials. The thickness of the third dielectric layer 240 isgreater than the thicknesses of the first and second dielectric layers235 and 237 in some embodiments.

A conductive contact 245 is formed in contact with the top electrode256, as shown in FIG. 9. The conductive contact 245 is the same as orsimilar to the lower metal wiring 213 and/or the via contact 219 and ismade of, for example, Cu, Al, Ta, Ti, Mo, Co, Pt, Ni, W, TiN and/or TaNand/or an alloy thereof or other suitable material.

As shown in FIG. 9, the upper surface of the top electrode 256 issubstantially flush with the upper surfaces of the first insulatingcover layer 227 and/or the second insulating cover layer 280 in someembodiments.

FIGS. 10A-15B show various stages of a sequential manufacturing processof a semiconductor device including an MRAM according to an embodimentof the present disclosure. It is understood that additional operationscan be provided before, during, and after processes shown by FIGS.10A-15F, and some of the operations described below can be replaced oreliminated, for additional embodiments of the method. Material,configuration, dimensions and/or processes the same as or similar to theforegoing embodiments described with FIGS. 1A-9 may be employed in thefollowing embodiments, and detailed explanation thereof may be omitted.

As shown in FIG. 10A, lower metal wirings 213 are formed in the firstILD layer 210 over the substrate 201. In some embodiments, via contacts207 are provided under the lower metal wirings 213. Then, as shown inFIG. 10B, a first insulating layer as an etch stop layer 220 is formedover the structure of FIG. 10A, and a second ILD layer 225 is formedover the first insulating layer 220. Further, as shown in FIG. 10B, viacontact openings 222 are formed to expose the upper surface of the lowermetal wirings 213, by using one or more lithography and etchingoperations. Subsequently, a via contact 219 including layers 215 and 217are formed, as shown in FIG. 10C. One or more film forming operations,such as CVD, PVD including sputtering, ALD, electro-chemical platingand/or electro-plating, are performed, and a planarization operation,such as CMP, is performed to fabricate the via contacts 219.

Then, as shown in FIG. 11A, a first conductive layer 254A for the bottomelectrode 254, a stacked layer 255A for the MTJ film stack 255 and asecond conductive layer 256A for the top electrode 256 are sequentiallyformed. In some embodiments, a hard mask layer 300 formed on the secondconductive layer 256A. The stacked layer 255A includes at least a firstmagnetic layer 130, a first non-magnetic material layer 135, a secondmagnetic layer 140 and a second and/or third non-magnetic material layer142, 145.

By using one or more lithography and etching operations, the film stackshown in FIG. 11A is patterned into an MRAM cell structure including thebottom electrode 254, the MTJ film stack 255 and the top electrode 256,as shown in FIG. 11B. In some embodiments, after patterning the secondconductive layer 256A, the stacked layer 255A and the first conductivelayer 256A, the second ILD layer 225 is partially recessed. The amountD1 of the recess is in a range from about 1 nm to about 30 nm in someembodiments.

Subsequently, as shown in FIG. 12A, a first insulating cover layer 227is formed to cover the MRAM cell structure. The first insulating coverlayer 227 can be formed by CVD, PVD or ALD or any other suitable filmdeposition method. In some embodiments, the first insulating cover layer227 is formed by CVD, PVD or ALD at a temperature range less than about150° C., such as a range from about 100° C. to about 150° C. When thefirst insulating cover layer 227 is formed at a higher temperature, suchas a range from about 200° C. to about 300° C. (or more), the filmformation process may cause damage to the MTJ film stack 255 since thefirst insulating cover layer 227 is directly formed on the MTJ filmstack 255. As shown in FIG. 12A, the first insulating cover layer 227 isconformally formed.

Then, as shown in FIG. 12B, a second insulating cover layer 280 isformed to cover the MRAM cell structure. The second insulating coverlayer 280 can be formed by CVD, PVD or ALD or any other suitable filmdeposition method. As shown in FIG. 12B, the second insulating coverlayer 280 is conformally formed. As set forth above, the secondinsulating cover layer 280 includes an aluminum-based insulatingmaterial in some embodiments. The aluminum-based insulating material,such as AlO (Al₂O₃), AlN, AlC, AlOC and AlON, can be formed by thefollowing operations. First, an aluminum layer is formed on the firstinsulating cover 227. The aluminum layer is formed by, for example,metal-organic CVD (MOCVD) or ALD using tri-methyl-aluminum (TMA). Then,a plasma treatment using NH₃, CO₂ and/or CO gases is performed over thealuminum layer, to convert the aluminum layer into AlO, AlN, AlC, AlOCor AlON. The concentrations of Al, O, C and/or N in the plasma treatedaluminum layer are not uniform, in particular, along the verticaldirection. The AlON layer may be made of two layers of AlO and AlN. Insome embodiments, a thin layer of aluminum having a thickness of lessthan about 1 nm remains at the bottom of the layer. A chemical oxidationof the aluminum layer using an oxidation solution may be employed. Insome embodiments, the AlO, AlOC, AlC, AlN and/or AlON layer can bedirectly formed by CVD, PVD or ALD or other suitable method by usingappropriate source gases. In some embodiments, the second insulatingcover layer 280 is formed by CVD, PVD or ALD at a temperature range in arange from about 300° C. to about 450° C. Although a lower formingtemperature (e.g., less than 300° C.) may be employed, since the firstinsulating cover layer 227 covers the MTJ film stack 255, a higherforming temperature (about 300° C. to about 450° C.) may not damage theMTJ film stack 255. In some embodiments, dielectric material other thanaluminum-based insulating material (e.g., silicon nitride, SiC, SiON orSiCN) is used as the second insulating cover layer 280. In someembodiments, the second insulating cover layer 280 is not used.

Next, as shown in FIG. 13A, a dielectric material layer 230A for thethird ILD layer 230 is formed to fully cover the second insulating coverlayer 280. In some embodiments, an etch-back operation is performed onthe dielectric material layer 230A, and then a CMP operation isperformed, as shown in FIG. 13B. Because the selectivity for the CMPoperation between the second insulating cover layer 280 and the thirdILD layer 230 is high, the CMP operation can utilize the secondinsulating cover layer 280 as a stop layer. When the CMP operation stopsat the upper surface of the second insulating cover layer 280, it ispossible to prevent over-etching of the third ILD layer 230, and thusthe upper surface of the second insulating cover layer 280 above theMRAM cell structure is substantially flush with the upper surfaces ofthe third ILD layer 230 in some embodiments.

Subsequently, as shown in FIG. 14A, a fourth ILD layer including a firstdielectric layer 235, a second dielectric layer 237 and a thirddielectric layer 240 is formed over the structure of FIG. 14B. Thedielectric layers of the fourth ILD layer can be formed by CVD, PVD orALD or other suitable film formation method. In some embodiments, thethird dielectric layer 240 is formed through a process such as CVD,flowable CVD (FCVD), or a spin-on-glass process, although any acceptableprocess may be utilized. Subsequently, a planarization process, such aschemical mechanical polishing (CMP) and/or an etch-back process, or thelike is performed.

Then, as shown in FIG. 14B, contact openings 242 are formed by using oneor more lithography and etching operations. Because the selectivity inthe etching operation between the second insulating cover layer 280 andthe fourth ILD layer is high, the etching operation can utilize thesecond insulating cover layer 280 as an etch stop layer.

Next, as shown in FIGS. 15A and 15B, a part of the second insulatingcover layer 280 and a part of the first insulating cover layer 227 areremoved by dry and/or wet etching, thereby exposing the top electrode256. In some embodiments, part of the second insulating cover layer 280is removed, and then part of the first insulating cover layer 227 isremoved. In some embodiments, one or more wet etching operations isused. In certain embodiments, a wet etching operation is performed toremove the second insulating cover layer 280 and a dry etching operationis performed to remove first insulating cover layer 227. In otherembodiments, a wet etching operation is also performed to remove thefirst insulating cover layer 227. By using wet etching, it is possibleto suppress damage to the MTJ film stack 255.

Subsequently, as shown in FIG. 15B, the contact openings 242 are filledwith a conductive material so as to form conductive contacts 245contacting the exposed top electrode 256.

It is understood that the device shown in FIG. 11B undergoes furthersemiconductor processes to form various features such as interconnectmetal layers, dielectric layers, passivation layers, etc.

It will be understood that not all advantages have been necessarilydiscussed herein, no particular advantage is required for allembodiments or examples, and other embodiments or examples may offerdifferent advantages.

In the present embodiments, a plurality of magnetic material pieces areused as a free magnetic layer (a segregated layer). This structure canchange the nature of the free magnetic layer design from a defaultsingle domain to default multiple domains. If the size of the domains,or grains, is much smaller than the device CD (e.g., a cell size) andthe magnetic material pieces are tightly distributed, device CDscale-down will have no obvious impact on the property distribution. Forexample, when the current density to switch the free magnetic layer (Jc)and the resistivity of the free magnetic layer (Ra) are the same, thewrite current, voltage and power can be decreased (scaled-down) with thetotal cross section of the magnetic grains. For that reason, thesegregated free magnetic layer structure can have a smaller writecurrent, voltage and power.

In accordance with an aspect of the present disclosure, in a method ofmanufacturing a magnetic random access memory (MRAM) cell, a firstmagnetic layer is formed over a substrate. A first non-magnetic materiallayer is formed over the first magnetic layer. A second magnetic layeris formed over the first non-magnetic material layer. A secondnon-magnetic material layer is formed over the second magnetic layer.The second non-magnetic material layer, the second magnetic layer, thefirst non-magnetic material layer and the first magnetic layer arepatterned, thereby forming the MRAM cell. The second magnetic layer inthe MRAM cell includes a plurality of magnetic material pieces separatedfrom each other. In one or more of the foregoing and followingembodiments, the plurality of magnetic material pieces are separatedfrom each other by a non-magnetic material. In one or more of theforegoing and following embodiments, a third non-magnetic material layeris further formed over the second magnetic layer before forming thesecond non-magnetic material layer, thereby separating the plurality ofpieces of magnetic material. In one or more of the foregoing andfollowing embodiments, the non-magnetic material of the secondnon-magnetic material layer is same as the non-magnetic materialseparating the plurality of pieces of magnetic material. In one or moreof the foregoing and following embodiments, the non-magnetic material ofthe second non-magnetic material layer is different from thenon-magnetic material separating the plurality of pieces of magneticmaterial. In one or more of the foregoing and following embodiments, thenon-magnetic material separating the plurality of magnetic materialpieces is a dielectric material. In one or more of the foregoing andfollowing embodiments, the third non-magnetic material layer is formedin direct contact with the first non-magnetic material layer. In one ormore of the foregoing and following embodiments, sizes of the pluralityof magnetic material pieces in plan view are random. In one or more ofthe foregoing and following embodiments, heights of the plurality ofmagnetic material pieces are random. In one or more of the foregoing andfollowing embodiments, a thickness of the second magnetic layer is in arange from 0.2 nm to 1.5 nm. In one or more of the foregoing andfollowing embodiments, a size of each of the plurality of magneticmaterial pieces in plan view is in a range from 1 nm to 10 nm. In one ormore of the foregoing and following embodiments, spaces between adjacentpieces of magnetic material in plan view are in a range from 0.2 nm to 5nm. In one or more of the foregoing and following embodiments, each ofthe plurality of magnetic material pieces has one magnetic domain.

In accordance with another aspect of the present disclosure, in a methodof manufacturing an MRAM cell, a first magnetic layer is formed over asubstrate, a first non-magnetic material layer is formed over the firstmagnetic layer, a second magnetic layer is formed over the firstnon-magnetic material layer and a second non-magnetic material layer isformed over the second magnetic layer and in direct contact with thefirst non-magnetic material layer. The second non-magnetic materiallayer, the second magnetic layer, the first non-magnetic material layerand the first magnetic layer are patterned, thereby forming the MRAMcell. The second magnetic layer in the MRAM cell includes a plurality ofislands of magnetic material separated from each other. In one or moreof the foregoing and following embodiments, the plurality of islands ofmagnetic material are separated from each other by the secondnon-magnetic material layer. In one or more of the foregoing andfollowing embodiments, a thickness of the second non-magnetic materiallayer is greater than a largest height of the plurality of islands ofmagnetic material. In one or more of the foregoing and followingembodiments, the second non-magnetic material layer is made of MgO. Inone or more of the foregoing and following embodiments, each of theplurality of islands of magnetic material has one magnetic domain.

In accordance with another aspect of the present disclosure, in a methodof manufacturing an MRAM cell, a first magnetic layer is formed over asubstrate, a first non-magnetic material layer is formed over the firstmagnetic layer, a second magnetic layer is formed over the firstnon-magnetic material layer, an annealing operation is performed on thesecond magnetic layer, and a second non-magnetic material layer isformed over the second magnetic layer. The second non-magnetic materiallayer, the second magnetic layer, the first non-magnetic material layerand the first magnetic layer are patterned, thereby forming the MRAMcell. The second magnetic layer in the MRAM cell includes a plurality ofmagnetic material pieces separated from each other. In one or more ofthe foregoing and following embodiments, an annealing temperature of theannealing operation is in a range from 400° C. to 800° C.

In accordance with one aspect of the present disclosure, a semiconductordevice includes a magnetic random access memory (MRAM) cell. The MRAMcell includes: a first magnetic layer disposed over a substrate, a firstnon-magnetic material layer made of a non-magnetic material and disposedover the first magnetic layer, a second magnetic layer disposed over thefirst non-magnetic material layer, and a second non-magnetic materiallayer disposed over the second magnetic layer. The second magnetic layerincludes a plurality of magnetic material pieces separated from eachother. In one or more of the foregoing and following embodiments, theplurality of magnetic material pieces are separated from each other by anon-magnetic material. In one or more of the foregoing and followingembodiments, a non-magnetic material of the second non-magnetic materiallayer is same as the non-magnetic material separating the plurality ofpieces of magnetic material. In one or more of the foregoing andfollowing embodiments, a non-magnetic material of the secondnon-magnetic material layer is different from the non-magnetic materialseparating the plurality of pieces of magnetic material. In one or moreof the foregoing and following embodiments, a non-magnetic material ofthe first non-magnetic material layer is same as the non-magneticmaterial separating the plurality of pieces of magnetic material. In oneor more of the foregoing and following embodiments, a non-magneticmaterial of the first non-magnetic material layer is different from thenon-magnetic material separating the plurality of pieces of magneticmaterial. In one or more of the foregoing and following embodiments, thefirst non-magnetic material layer, the second non-magnetic materiallayer and the non-magnetic material separating the plurality of magneticmaterial pieces are made of a same material. In one or more of theforegoing and following embodiments, the non-magnetic materialseparating the plurality of magnetic material pieces is a dielectricmaterial. In one or more of the foregoing and following embodiments, thedielectric material is magnesium oxide. In one or more of the foregoingand following embodiments, sizes of the plurality of magnetic materialpieces in plan view are random. In one or more of the foregoing andfollowing embodiments, heights of the plurality of magnetic materialpieces are random. In one or more of the foregoing and followingembodiments, a thickness of the second magnetic layer is in a range from0.2 nm to 1.5 nm. In one or more of the foregoing and followingembodiments, a size of each of the plurality of magnetic material piecesin plan view is in a range from 1 nm to 10 nm. In one or more of theforegoing and following embodiments, spaces between adjacent of piecesof magnetic material in plan view are in a range from 0.2 nm to 5 nm. Inone or more of the foregoing and following embodiments, the plurality ofmagnetic material pieces has random magnetic directions. In one or moreof the foregoing and following embodiments, a ratio of areas of theplurality of magnetic material pieces covering the first non-magneticlayer to an area of the first non-magnetic layer is in a range from 0.5to 0.9. In one or more of the foregoing and following embodiments, eachof the plurality of magnetic material pieces has one magnetic domain. Inone or more of the foregoing and following embodiments, a width of eachof the plurality of magnetic material pieces is non-uniform along avertical direction.

In accordance with another aspect of the present disclosure, asemiconductor device includes an MRAM cell. The MRAM cell includes anMRAM cell structure disposed over a substrate. The MRAM cell structureincludes a bottom electrode, a magnetic tunnel junction (MTJ) stack anda top electrode. The MRAM cell structure includes a first insulatingcover layer covering sidewalls of the MRAM cell structure, a secondinsulating cover layer disposed over the first insulating cover layer, adielectric layer, and a conductive contact in contact with the topelectrode. The first insulating cover layer is made of a nitride-basedinsulating material. The second insulating cover layer is made of analuminum-based insulating material different from the nitride-basedinsulating material. The MTJ stack includes: a pinned magnetic layerdisposed over a substrate, a tunneling barrier layer disposed over thefirst magnetic layer, a free magnetic layer disposed over the tunnelingbarrier layer, and a capping layer disposed over the second magneticlayer. The second magnetic layer includes a plurality of islands ofmagnetic material separated from each other.

In accordance with another aspect of the present disclosure, an MRAMincludes a matrix of MRAM cells. The MRAM cell includes: a firstmagnetic layer disposed over a substrate, a first non-magnetic materiallayer made of a non-magnetic material and disposed over the firstmagnetic layer, a second magnetic layer disposed over the firstnon-magnetic material layer, and a second non-magnetic material layerdisposed over the second magnetic layer. The second magnetic layerincludes a plurality of magnetic material pieces separated from eachother by and embedded in the second non-magnetic material layer.

The foregoing outlines features of several embodiments or examples sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodiments orexamples introduced herein. Those skilled in the art should also realizethat such equivalent constructions do not depart from the spirit andscope of the present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A magnetic random access memory (MRAM),comprising: a first magnetic layer disposed over a substrate; a firstnon-magnetic layer disposed over the first magnetic layer; a secondmagnetic layer disposed over the first non-magnetic layer; a secondnon-magnetic layer disposed over the second magnetic layer; and a thirdnon-magnetic layer disposed in direct contact with the secondnon-magnetic layer, wherein: the second magnetic layer includes aplurality of magnetic material pieces separated from each other, all ofthe plurality of magnetic material pieces are in direct contact with thefirst non-magnetic layer, and when viewed from above, shapes of theplurality of magnetic material pieces includes a circular shape, an ovalshape and a cloud-shape.
 2. The MRAM of claim 1, wherein the pluralityof magnetic material pieces are separated from each other by the secondnon-magnetic layer.
 3. The MRAM of claim 2, wherein the secondnon-magnetic layer is made of magnesium oxide.
 4. The MRAM of claim 2,wherein a material of the second non-magnetic layer is same as amaterial of the third non-magnetic layer.
 5. The MRAM of claim 2,wherein a material of the second non-magnetic layer is different from amaterial of the third non-magnetic layer.
 6. The MRAM of claim 2,wherein the third non-magnetic layer includes at least one of magnesiumoxide, silicon oxide or aluminum oxide.
 7. The MRAM of claim 1, whereinthe second non-magnetic layer is formed in direct contact with the firstnon-magnetic material layer.
 8. The MRAM of claim 1, wherein a size ofeach of the plurality of magnetic material pieces in plan view is in arange from 0.5 nm to 20 nm.
 9. The MRAM of claim 1, wherein heights ofthe plurality of magnetic material pieces are random.
 10. The MRAM ofclaim 1, wherein a thickness of the second magnetic layer is in a rangefrom 0.2 nm to 1.5 nm.
 11. The MRAM of claim 1, wherein a size of eachof the plurality of magnetic material pieces in plan view is in a rangefrom 1 nm to 10 nm.
 12. The MRAM of claim 1, wherein spaces betweenadjacent pieces of magnetic material in plan view are in a range from0.2 nm to 5 nm.
 13. The MRAM of claim 1, wherein each of the pluralityof magnetic material pieces has one magnetic domain.
 14. A magneticrandom access memory (MRAM), comprising: a first magnetic layer disposedover a substrate; a first non-magnetic layer disposed over the firstmagnetic layer; a second magnetic layer disposed over the firstnon-magnetic layer; a second non-magnetic layer disposed over the secondmagnetic layer; and a third non-magnetic layer disposed in directcontact with the second non-magnetic layer, wherein: the second magneticlayer includes a plurality of magnetic material pieces separated fromeach other, all of the plurality of magnetic material pieces are indirect contact with the first non-magnetic layer, and each of theplurality of magnetic material pieces has a cross section shape selectedfrom the group consisting of a tapered columnar shape having a width ata top smaller than a width at a bottom, a reversed tapered columnarshape having a width at a top larger than a width at a bottom, acolumnar barrel shape having a largest width at a middle, and a columnarpincushion shape having a smallest width at a middle.
 15. The MRAM ofclaim 14, wherein the plurality of magnetic material pieces areseparated from each other by the second non-magnetic layer.
 16. The MRAMof claim 14, wherein the second non-magnetic layer is made of adielectric material.
 17. The MRAM of claim 14, wherein the secondnon-magnetic layer is amorphous.
 18. The MRAM of claim 14, wherein thesecond non-magnetic layer is crystalline or polycrystalline.
 19. Asemiconductor device including a magnetic random access memory (MRAM)cell, wherein the MRAM cell comprises: a magnetic random access memory(MRAM) cell structure disposed over a substrate, the MRAM cell structureincluding a bottom electrode, a magnetic tunnel junction (MTJ) stack anda top electrode; a first insulating cover layer covering sidewalls ofthe MRAM cell structure; a second insulating cover layer disposed overthe first insulating cover layer and layer made of a different materialthan the first insulating cover layer; and a dielectric layer disposedover the MRAM cell structure and the second cover layers, wherein theMTJ stack includes: a pinned magnetic layer disposed over the bottomelectrode; a tunneling barrier layer disposed over the pinned magneticlayer; a free magnetic layer disposed over the tunneling barrier layer;and a capping layer disposed over the free magnetic layer, the freemagnetic layer includes a plurality of islands of magnetic materialseparated from each other.
 20. The semiconductor device of claim 19,wherein the capping layer is in direct contact with the tunnelingbarrier layer.